Ballast for mercury vapor lamps



May 24, 1960 w. B. ELMER 2,938,145

BALLAST FOR MERCURY VAPOR LAMPS Filed June 19, 1958 2 Sheets-Sheet 1F/GZ ' INVENTOR. W/AZ/fl/V 6. [SAME/F 9 BY i C [Fromm-y May 24, 1960 w.B. ELMER 2,938,145

BALLAST FOR MERCURY VAPOR LAMPS Filed June 19, 1958 2 Sheets-Sheet 2 2 9INVENTOR.

177' MAWEY United States This invention relates to mercury vapor lampsand espe cially to the ballast feature thereof.

Mercury vapor lamps are usually equipped with ballasts of thetransformer type, which, however, have the disadvantage that theyinvolve a watt loss of percent or more of the lamp wattage. Furthermore,a ballast of this type for a 250 watt lamp in particular is relativelybulky and expensive.

One object of the present invention is to provide a novel ballast for amercury vapor lamp which can be made smaller and more compact than thetransformer type and which will involve a smaller watt loss when in useand will also be effective in starting the lamp even at extremely lowtemperatures.

Other objects and advantages of the invention will be apparent from thefollowing description in connection with the accompanying drawings, eachfigure of which illustrates a difierent embodiment of the invention.

Fig. 1 is a wiring diagram showing one embodiment of the invention;

Fig. 2 is a wiring diagram showing a different embodiment of theinvention;

Fig. 3 is a wiring diagram showing a third embodiment of the invention;and

Figs. 4 and 5 are wiring diagrams showing an embodiment of the inventionwhich includes two capacitors.

Referring to Fig. l, which shows a wiring diagram of a mercury vaporlamp circuit including the improved ballast, 2 indicatesdiagrammatically a mercury vapor lamp, and 3 and 4 are the two sides ofan alternating current power supply circuit which furnishes current tothe lamp 2 and which for convenience will be referred to as the supplyline.

6 indicates a control switch in the supply line by which the latter maybe opened and closed, said switch being shown as the single pole, singlecontact type and which comprises the pole or switch blade 7 and thesingle contact 8.

The ballast feature embodying the invention includes a reactance, hereinshown as choke coil 17, which, when switch 6 is closed, is connectedacross the supply line 3, 4 in series with the lamp 2 by means of thecircuit 5, and also includes a capacitor 9 which can be connected acrossthe supply line either in series with the choke coil 17 and in parallelwith the lamp 2, or in parallel with both the choke coil and the lamp.

The means by which the capacitor may be thus connected, either in serieswith the choke coil or in parallel therewith, may be in the form of asingle pole, double throw relay, the relay coil of which,, shown at 18,is connected in series with both the choke coil 17 and the lamp 2, asillustrated in Fig. l. The switch portion of this relay includes asingle pole 11 which is adapted to contact either one of the twocontacts 13 and 14. The contact 13 is connected by wire 15 with thecircuit connection 5 at a point between the choke coil 17 and the relaycoil 18. The contact 14 is connected by a wire connection 16 .with theside 4 of the supply line when switch 6 is closed.

atent Patented May 24, 1960 The pole 11 of the switch is connected bywire 10a with one terminal of the capacitor 9, and the other terminal ofthe said capacitor is connected to the side 3 of the supply line by thewire 10.

The relay is so constructed that when the coil 18 is deenergized, theswitch will be set as shown in full lines, Fig. 1, thereby connectingthe capacitor in series'with the choke coil 17. When the relay coil 18is energized, the pole of the switch will be thrown over into the dottedline position, Fig. 1, thereby connecting the capacitor 9 in parallelwith the choke coil.

A capacitor 9 should be used in the construction shown which has agreater reactance value than that of the reactor or choke coil 17.

When the control switch 6 is open, as shown in Fig. 1, there will be nocurrent flow through the circuit 5, and

hence the relay coil 18 will be de-energized and the switch 12 will beset, as shown in full lines, Fig. 1, thus connecting the choke coil inseries with the capacitor. 1

If, when the switch 6 is closed, the lamp 2 does not strike due to lowtemperature, there will be nocurrent flow through the relay coil 13; andthe latter will remain de-energized so that the switch 12 remains set asshown in Fig. 1. With the capacitor 9 having a greater capactivereactance than the inductive reactance of the choke coil 17, these twoelements, being connected in series, will build up a voltage across thelamp greater than the normal line voltage. The reactance value ofcapacitance 9 is selected sufficiently low to cause the lamp to strikedown to a predetermined low temperature limit for the lamp. The rise involtage produced by the series connection of a capacitor and reactoracross an AC. electric supply line is 'well known to those skilled inthe art. As soon as the lamp strikes, current will flow through therelay coil 18 and the lamp, thus energizing said coil and causing theswitch pole 11 to be thrown over against contact 14, thereby removingthe capacitor from the choke coil circuit and placing it across thesupply line in parallel with said choke coil. The lamp 2 will then passthrough its warming-up stages and into its normal operating condition.

By using a capacitor having the proper reactance value relative to thatof the choke coil, the construction above described would be effectivein lighting the mercury vapor lamp at temperatures as low as minus 20 F.

As long as the lamp is lighted and there is sufiicient current flowthrough the lamp circuit 5, the relay coil will remain energized,thereby holding the switch pole 11 in engagement with the contact 14.

If, however, there is an interruption in the supply of current to thelamp, or if there is a voltage dip across the line sufficient toextinguish the lamp, the relay coil will become de-energized and theswitch pole 11 will return to its normal position shown in full lines,Fig. 1, thus placing the capacitor again in series with the choke coil18 and in position to cooperate with said choke coil in starting thelamp again when the current supply is resumed or when the lamp hascooled sufiiciently to restrike.

In a case where the lamp is extinguished by a dip in voltage across theline, the placing of the capacitor in series with the choke coil, asabove described, will build up sufiicient voltage across the lamp torestart it in less lamp-cooling time than that required withconventional ballast systems. 7

In Fig. 2 there is shown an embodiment of the invention in which thecapacitor 9 is normally connected across the supply line in parallelwith the series combination of the choke coil 17 and the lamp 2, evenwhen the control switch is open. In this embodiment, however, provisionis made for connecting the capacitor in series with the choke coilwhenever the control switch 6 is closed, thereby placing the capacitorin position to cooperate with the choke coil in starting the lamp in themanner corresponding to that described with reterence to Fig. 1.

The means by which the capacitor may be connected across; the s pply nith r n eriesor in p a e t hechcke oil, n l d s re y s tch 20, e coi efiwhic is indica ed t .5. T s w tch, s. o th sin e p l w contact type,having the pole or switch blade 22 and two contacts 21 and 2:3- The o tat: 13. s; co ne ted by a w re on c io 2 i h t e s de 4 o the upp y lineat a pointa y the. upp y side of t e s itchv 6.. T e. c nt ct- 21 isconnected by circuit: connection 26 to the lamp circuit -5 at a pointbetween the, choke coil 17 and the lamp. The pole 2 2 is connected toone terminal of the capacitor, as shown at 28, and the other terminal ofsaid capacitor is; connected, to the side 3 of the.- supply line, by thecircuit conne ion 29.

The relay coil 25 is connected in series withthe choke coil but inparallel withthe. lamp by means of the circuit connection 27.

The relay switch is so constructed that when coil 25 thereof is(la-energized, the pole of the switch 20 will contact element 23, asshown in full lines, Fig. 2', so that the capacitor is connected acrossthe line in parallel with both the choke coil and lamp.

If, when the control switch t5- is closed to light the lamp 2, sa dampdo s n mmediately str e, there ill e a urr ntflc thr u h. the h k coil17 and. t e r l y il 25; and the, latter will be subjected tosubstantially the full voltage of the supply line. This is sufficient toenergize the coil 25 so that; it becomes operative to swing the switchpole 22 from the full line position, Fig, 2, into the, dotted lineposition, thereby connecting the capacitor in series with the choke coiland establishing its parallel relation to the lamp. As soon as thecapacitorand choke coil; are connected in series, they cooperate witheach other as above described with reference to the construction shownin Fig. l to build up voltage across the lamp 2- which becomessufiicient, to cause it to strike, even in cold weather.

As soon as the lamp has started, the voltage across it,

and consequently across the relay coil 25, will drop to a lowValuer-below that at which the relay coil is effective in holding theswitch pole 22 in engagement with the contact 21. And when thiscondition arises, the relay will not be strong enough to maintain theswitch pole 22 in engagement with said contact 21, and said switch polewill return to its normal position shown in full lines, Fig. 2,,therebyagain connecting the, capacitor across the line in parallel with thechoke coil and; the lamp.

- The relay is so constructed that the voltage across the lamp and therelay after the lamp has warmed up and is functioning normally is lessthan that required to return the switch pole to the dotted lineposition, Fig. 2, so that after the lamphas started and isoperatingnormally, the capacitor will remain connected across the supply line inparallel with the choke coil during the time that the lamp isfunctioning normally.

It will be observed that, with the construction shown in Fig. 2, whereinthe capacitor 9 is connected to the side 4 of the supply circuit at apoint on the supply side of the control switch 6, the capacitor will beconnected across the supply line in parallel with both the choke coiland the lamp practically 24 hours a day whether the control switch 6 isopen or closed. The only time when said capacitor is not so connected inseries with the choke coil is during the relatively short time interval,while the lamp 2 is getting started.

When the capacitor 9 is connected across the supply line, as shown inFig. 2, it is in a position to function as a means for power-factorconnection; and with the circuit connection shown in Fig. 2, saidcapacitor would thus function all the time whether the control switch 6is open or closed except during the relatively short interval when it isconnected in series with the choke coil 17 for starting the lamp.

The embodiment of. he. inyention sho n in igi similar to that shown inFig, 2 except that the capacitor circuit is connected to the side 3 ofthe power line on the load side of the switch 6 instead of on the supplyside thereof, as shown in Fig. 2. With this construction, the capacitorcould not perform its function of power-factor correction except whenthe control switch is closed. This arrangement is preferred when noother electric loads of any inductive. type. exist on the. supply:circuit. So. far as the starting of the lamp is concerned, the. deviceillustrated in Fig. 3 functions, whenever the control switch 6 isclosed, exactlythe same as that illustrated in Fig. 2.

The voltage rating of the capacitor 9 is selected to equal or exceed thelamp-starting-voltage produced by the starting circuit described above.Said voltage is in excess of that required for a capacitor that isconnected across the supply circuit permanently for power-factorcorrection.

The amount of capacitance in. microfaliads: required. to correct the,power; factor of; the lamp and ballast combination to greater than 9.0percentis usually greater than the amount; required to start the, lampin: accordance with the, present invention. If itis desired toaccomplish the dual purpose of lamp starting in, cold; weather and alsopower-factor correction, the capacitor size.- inmicrofarads can. beincreased he nece sary alue. tov acc mp both o j c sv Elms ven if uch dal purp is ired. itmay; be; advantageous to use two separate capacitors,9 and 941-, as shown in Fig. 5,. In; this construction, the capacitor 9ais connected permanently across the supply line by the wire connection30; and its sole purpose may be that of power-factorcorrection. Inthis-case, the voltage rating of the, capacitor 9a can; be less thanthat of the capacitor 9, which must have a voltage rating equal to orexceeding the lamp-starting voltage. The use of the two capacitors; mayresult in a more economical construction than that involved in using asingle lamp capacitor of, higher voltage. rating.

It is also possible to use the second capacitor 9a in the constructionshown in Fig. l, as illustrated. in Fig. 4. In this case, the secondcapacitor 9a willbe permanently connected across the supply line and is;operative; for powerfactorcorrection continuously whenever the switch 6is closed. I

Some: of; the advantages which the, ballast system herein described hasover the conventional; transformer type are hat a llast, y t m embodyingthe present inv n ion i bstantially ess: exp nsive; to. manufacture nd.is m r c mical; in use than. the ransform r on ention l typ especiallywith the larger lamp sizes from 250 watts up.

Furthermore, asballast system; as herein disclosed will cause the lamp,tov strike after a circuit interruption; or voltage dip; in .a;-substantially, shorter time than the conventional ballast systems now,in use. If; it is desired to reduce the restriking time of the lamp toless than that n ounter with: y! old-weather: starting; circuit, thevalue of capacitance caliber increased to values approaching but not;reaching the conditionv of resonance; that is, the condition in whichthe specificv capacitive reactance of the. capacitor is; equal to thespecific inductive reactance of the reactonwhich condition would resultin insufiicient total circuit impedance and circuit. overcurrent.conditions with loss of ballasting effect and. destruction of the lamp.Therefore, the capacitor 9 should not be increased to the resonantcondition. It may, however, be increased to produce a lamp startingvoltage exceeding that required for cold weather starting in order toachieve sharter restriking time after a supply circuit interruption.Voltage dips or brief supply circuit interruptions will thus resultinshorter intervals of lamp-extinction and reduced danger to the publicwhen. the street lamp is: temporarily out ofoperation.

The control switch GLcanbe of any-type-without departingfrom theinvention. Ifit is of the photoelectric type,

incorporated into a luminairc, the connection shown in Fig. 2 can bepre-wired completely within the luminaire along with all othercomponents, in which case it would be only necessary to connect thesupply wires to the luminaire assembly to place the unit in completeoperation.

I claim.

1. The combination with an electrical supply line, of a vapor lamp and achoke coil connected in series across the supply line, a control switchfor closing and opening the lamp circuit, a capacitor having animpedance higher than that of choke coil, means connecting thecap-acitor across the supply line in series with the choke coil and inparallel with the lamp, whereby when the control switch is closed toignite the lamp, the series connection of the choke coil and capacitorbuilds up voltage across the lamp sufficiently greater than the normalline voltage to ignite the lamp at temperatures below those at which thenormal line voltage would be efiective for that purpose.

2. The combination with an electrical supply line, of a vapor lamp and achoke coil connected in series across the supply line, a control switchfor closing and opening the lamp circuit, a capacitor having animpedance higher than that of the choke coil, means connecting thecapacitor across the supply line in series with the choke coil and inparallel with the lamp, whereby when the control switch is closed toignite the lamp, the series connection of the choke coil and capacitorbuilds up voltage across the lamp suificiently greater than the normalline voltage to ignite the lamp at temperatures below those at which thenormal line voltage would be effective for that purpose, and meansrendered operative by the current passing through the choke coil afterthe lamp is ignited to open the series connection between the choke coiland the capacitor and to connect the latter across the line.

3. The combination with an electrical supply line, of a vapor lamp andchoke coil, means including a lamp circuit connecting the vapor lamp andchoke coil in series across the supply line, a control switch foropening and closing the lamp circuit, a capacitor having an impedancehigher than that of the choke coil and normally connected across thesupply line in parallel with both the choke coil and the lamp, a relayconnected across the supply line in series with the choke coil and inparallel with the lamp, whereby when the control switch is closed forthe purpose of starting the lamp and the lamp does not strike, the relaywill be energized, and means actuated by the energized relay to breakthe parallel relationship between the choke coil and the capacitor andto'connect the capacitor in series with the choke coil, thereby to buildup a suiiicient voltage across the lamp to eifect ignition thereof.

4. The combination with an electrical supply line, of a vapor lamp and avapor lamp ballast, means including a lamp circuit connecting said lampand ballast across the supply line, said ballast including a capacitorand choke coil, the capacitor having an impedance greater than that ofthe choke coil, a control switch for opening and closing the lampcircuit, and means to connect the capacitor to the supply line forpower-factor correction when the control switch is open.

5. The combination with an electrical supply line, of

a vapor lamp and a vapor lamp ballast having a capacitor and a chokecoil, means including a lamp circuit for connecting said vapor lamp andvapor lamp ballast across the supply line, said ballast containingcapacitance sufiicient for power-factor correction and having animpedance greater than the impedance of the choke coil, a control switchmeans for opening and closing the lamp circuit, and means for connectingsaid capacitance to the electrical supply circuit on the supply side ofthe control switch whereby said capacitance will be operative forpower-factor correction when said control switch is open.

6. The combination with an electrical supply line, of a vapor lamp and achoke coil, means, including a lamp circuit, connecting the vapor lampand choke coil in series across the supply line, a control switch foropening and closing the lamp circuit, a two-part capacitor, one part ofwhich has an impedance higher than that of the choke coil, meansnormally connecting said capacitor across the supply line in parallelwith both the choke coil and the lamp, a relay connected across thesuply line in series with the choke coil and in parallel with the lamp,whereby when the control switch is closed for the purpose of startingthe lamp and the lamp does not strike, the relay will be energized, andmeans actuated by the energized relay to break the parallel relationshipbetween said one part of the capacitor and the choke coil and to connectsaid one part of the capacitor in series with the choke coil, thereby tobuild up sufiicient voltage across the lamp to eflect ignition thereof.

7. The combination with an electrical supply line, of a vapor lamp and avapor lamp ballast, having a capacitor and a choke coil, means includinga lamp circuit for connecting said vapor lamp and vapor lamp ballastacross the supply line, said ballast containing capacitance sufficientfor power-factor correction and having an impedance greater than theimpedance of the choke coil, control means for opening and closing thelamp circuit, and means for connecting said capacitance to theelectrical supply circuit for power-factor correction when the lampcontrol means is in the closed condition.

8. The combination with an electrical supply line, of a vapor lamp and achoke coil, means, including a lamp circuit, connecting the vapor lampand choke coil in series across the supply line, a control switch foropening and closing the lamp circuit, a two-part capacitor, one part ofwhich has an impedance higher than that of the choke coil, meansnormally connecting said capacitor in parallel with said vapor lamp andchoke coil, a relay connected across the supply line in series with thechoke coil and in parallel with the lamp, whereby when the controlswitch is closed for the purpose of starting the lamp and the lamp doesnot strike, the relay will be energized, and means actuated by theenergized relay to break the parallel relationship between said one partof the capacitor and the choke coil and to connect said one part of thecapacitor in series with the choke coil, thereby to build up sufficientvoltage across the lamp to eifect ignition thereof.

References Cited in the file of this patent UNITED STATES PATENTS2,182,609 Bethenod Dec. 5, 1939

